Impeller and rotary machine

ABSTRACT

An impeller includes a hub having a circular plate shape with an axial line as a center, a shroud disposed to face the hub in a direction of the axial line, and a plurality of blades disposed with a space from each other in a circumferential direction between the hub and the shroud. A meridian plane shape of the impeller differs in the circumferential direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2022-015795 filed in Japan on Feb. 3, 2022.

FIELD

The present disclosure relates to an impeller and a rotary machine.

BACKGROUND

As a rotary machine, there is a centrifugal compressor with an impeller housed inside. The centrifugal compressor applies pressure energy and velocity energy to a fluid by rotating the impeller. As the impeller used for the centrifugal compressor, there is a closed impeller in which a plurality of blades are disposed between a hub and a shroud. One example of the closed impeller is described in the following patent literature.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 3299638

SUMMARY Technical Problem

A general closed impeller has a spiral-shaped flow channel from an inlet at the central side to an outlet at an outer peripheral part. Since the flow channels are provided in a radial shape, the passage area tends to expand rapidly toward the outer peripheral part, causing the fluid to separate easily, and thus, loss easily occurs. In view of this, it is considered to gradually increase the thickness of the blade from the inlet to the outlet so as to suppress the rapid expansion of the passage area. However, if the thickness of the blade is gradually increased from the inlet to the outlet, a plurality of the outlets are interrupted in a circumferential direction by the thickness of the blade. Then, the pressure of the fluid discharged from the respective outlets in the outer peripheral part fluctuates in the circumferential direction, resulting in a problem of pressure pulsations.

The present disclosure is to solve the above problem, and it is an object to provide an impeller and a rotary machine in which the occurrence of pressure pulsations is suppressed by reducing pressure fluctuations at an outlet.

Solution to Problem

To achieve the object, an impeller according to the present disclosure includes: a hub having a circular plate shape with an axial line as a center; a shroud disposed to face the hub in a direction of the axial line; and a plurality of blades disposed with a space from each other in a circumferential direction between the hub and the shroud, wherein a meridian plane shape of the impeller differs in the circumferential direction.

A rotary machine according to the present disclosure includes the above-described impeller.

Advantageous Effects of Invention

According to the impeller and the rotary machine of the present disclosure, pressure pulsations can be suppressed by reducing pressure fluctuations at the outlet.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a main part of a rotary machine in which an impeller according to one embodiment is used.

FIG. 2 is a front view of the impeller.

FIG. 3 is a cross-sectional view at a position of an arrow III in FIG. 2 , illustrating a meridian plane shape of an upper half part of the impeller according to the embodiment.

FIG. 4 is a cross-sectional view at a position of an arrow IV in FIG. 2 , illustrating the meridian plane shape of the upper half part of the impeller according to the embodiment.

FIG. 5 is a cross-sectional view at a position of an arrow V in FIG. 2 , illustrating the meridian plane shape of the upper half part of the impeller according to the embodiment.

FIG. 6 is a cross-sectional view at a position of an arrow VI in FIG. 2 , illustrating the meridian plane shape of the upper half part of the impeller according to the embodiment.

FIG. 7 is a side view of a main part of the impeller, illustrating an outlet of the impeller according to the embodiment.

FIG. 8 is a schematic view illustrating the blade shape on a hub side in the impeller.

FIG. 9 is a schematic view illustrating the blade shape in a middle part between a hub and a shroud in the impeller.

FIG. 10 is a schematic view illustrating the blade shape of on a shroud side in the impeller.

FIG. 11 is a side view of a main part of an impeller according to a first modification, illustrating an outlet of the impeller.

FIG. 12 is a side view of a main part of an impeller according to a second modification, illustrating an outlet of the impeller.

FIG. 13 is a side view of a main part of an impeller according to a third modification, illustrating an outlet of the impeller.

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of the present disclosure is described in detail below with reference to the drawings. The present disclosure is not limited by this embodiment, and if there is more than one embodiment, the embodiments may be configured in combination. The components in the embodiment include those that can be easily conceived by those skilled in the art, those that are substantially the same, and those that are in the so-called range of equivalence.

EMBODIMENT Centrifugal Compressor

FIG. 1 is a cross-sectional view of a meridian plane shape of an upper half part of an impeller used for a rotary machine. In the description of the present embodiment, a centrifugal compressor is used as the rotary machine.

As illustrated in FIG. 1 , a centrifugal compressor 10 includes a casing 11, a rotary shaft 12, and an impeller 13. The centrifugal compressor 10 applies pressure energy and velocity energy to a working fluid (such as a liquid or gas) by rotating the impeller 13.

The casing 11 houses a part of the rotary shaft 12 and the impeller 13. The casing 11 has a long tubular shape in a direction in which an axial line O of the rotary shaft 12 extends (hereinafter referred to as an axial direction Da). The casing 11 includes a first space part 21 that has a columnar shape along the axial direction Da and a second space part 22 that has a circular plate shape expanding in a direction orthogonal to the axial direction Da (hereinafter referred to as a radial direction Dr). A plurality of the second space parts 22 are arranged with a space from each other in the axial direction Da of the first space part 21. The first space part 21 and the second space parts 22 communicate with each other. The first space part 21 houses the rotary shaft 12, and the second space parts 22 each house the impeller 13.

The casing 11 includes an inlet passage 23 for introducing a working fluid G into the impeller 13 on one side in the axial direction Da (left side in FIG. 1 ). The casing 11 includes an outlet passage 24 for discharging the working fluid G from the impeller 13 on one side in the radial direction Dr (upper side in FIG. 1 ). The outlet passage 24 bends toward the axial line O so that the downstream side forms a U-shape, and then bends along the other side in the axial direction Da (right side in FIG. 1 ) so as to form an L-shape. In other words, the outlet passage 24 has a diffuser part, a return bend part, and a return flow channel on the downstream side although not illustrated. In the outlet passage 24, the return flow channel communicates with the inlet passage 23 of the impeller 13 that is adjacent in the axial direction Da.

The rotary shaft 12 is supported so as to be rotatable around the axial line O with respect to the casing 11. The rotary shaft 12 has both ends in the axial direction Da rotatably supported by bearings (not illustrated) with respect to the casing 11. The impeller 13 is fixed to the rotary shaft 12. The impeller 13 rotates together with the rotary shaft 12. The impeller 13 compresses the working fluid G using centrifugal force.

Basic Configuration of Impeller

FIG. 2 is a front view of the impeller.

As illustrated in FIG. 1 and FIG. 2 , the impeller 13 is a closed impeller including a hub 31, a shroud 32, and a plurality of blades 33. The impeller 13 has a structure in which the blades 33 are disposed with a space (preferably equal space) from each other in the circumferential direction Dc between the hub 31 and the shroud 32. The blades 33 are fixed to the hub 31 on one side in the axial direction Da and to the shroud 32 on the other side. The impeller 13 includes a plurality of impeller flow channels 34 surrounded by the hub 31, the shroud 32, and the blades 33. The impeller flow channel 34 is arranged so as to bend about 90 degrees from the axial line O side to the outer peripheral part side and form a spiral shape with the axial line O as the center.

The hub 31 has a circular plate shape with the axial line O as the center. The hub 31 gradually expands outward in the radial direction Dr from one side to the other side in the axial direction Da. The hub 31 has a circular through-hole 41 that passes through in the axial direction Da at the position of the axial line O corresponding to the center part. The hub 31 is fixed integrally to the rotary shaft 12 with an inner peripheral surface of the through-hole 41 fitted to an outer peripheral surface of the rotary shaft 12.

The hub 31 has a main surface 42 formed on one side in the axial direction Da. The main surface 42 expands outward in the radial direction Dr from one side to the other side in the axial direction Da. The main surface 42 faces outward in the radial direction Dr in a part on one side in the axial direction Da and faces one side in the axial direction Da in a part on the other side in the axial direction Da. In other words, the main surface 42 forms a concave curved surface shape by curving so as to face one side in the axial direction Da in a direction from one side to the other side in the axial direction Da.

The shroud 32 is disposed apart from the hub 31 by a predetermined distance to the other side in the axial direction Da. The shroud 32 gradually expands outward in the radial direction Dr from one side to the other side in the axial direction Da. The shroud 32 has an opposing surface 43 on the other side Dad in the axial direction Da. The opposing surface 43 expands outward in the radial direction Dr from one side to the other side in the axial direction Da. The opposing surface 43 faces outward in the radial direction Dr in a part on one side in the axial direction Da and faces the other side in the axial direction Da in a part on the other side in the axial direction Da. In other words, the opposing surface 43 forms a convex curved surface by curving so as to face the other side in the axial direction Da in a direction from one side to the other side in the axial direction Da.

The blade 33 connects between the hub 31 and the shroud 32. The blade 33 is fixed to the main surface 42 of the hub 31 on one side in the axial direction Da and fixed to the opposing surface 43 of the shroud 32 on the other side in the axial direction Da. The blade 33 extends to bend from one side in the axial direction Da to the outside in the radial direction Dr. The blades 33 are disposed with a space therebetween in the circumferential direction Dc around the axial line O. The blades 33 are arrayed radially to the outside in the radial direction Dr with the axial line O as the center. The blade 33 curves toward the rear in the rotating direction of an impeller 13 in a direction from the inner side in the radial direction Dr to the outer side in the radial direction Dr.

The impeller flow channel 34 is formed in a manner of being divided into a plurality of sections in the circumferential direction Dc by the blades 33 between the hub 31 and the shroud 32. The impeller flow channel 34 extends while curving from the inside to the outside in the radial direction Dr in a direction from one side to the other side in the axial direction Da. The impeller flow channel 34 has an inlet 44 that opens on one side in the axial direction Da and on the inside in the radial direction Dr. The impeller flow channel 34 has an outlet 45 that opens on the other side in the axial direction Da and on the outside in the radial direction Dr. The inlet 44 communicates with the inlet passage 23, and the outlet 45 communicates with the outlet passage 24.

Meridian Plane Shape of Impeller

FIG. 3 is a cross-sectional view at a position of an arrow III in FIG. 2 , illustrating a meridian plane shape of an upper half part of the impeller according to the embodiment. FIG. 4 is a cross-sectional view at a position of an arrow IV in FIG. 2 , illustrating the meridian plane shape of the upper half part of the impeller according to the embodiment. FIG. 5 is a cross-sectional view at a position of an arrow V in FIG. 2 , illustrating the meridian plane shape of the upper half part of the impeller according to the embodiment. FIG. 6 is a cross-sectional view at a position of an arrow VI in FIG. 2 , illustrating the meridian plane shape of the upper half part of the impeller according to the embodiment.

The impeller 13 is a closed impeller including the hub 31, the shroud 32, and the blades 33, and the hub 31, the shroud 32, and the blades 33 form the impeller flow channels 34. The impeller 13 varies in meridian plane shape in the circumferential direction Dc.

In other words, in the impeller flow channels 34 of the impeller 13 that are sectioned by the hub 31, the shroud 32, and the blades 33, the positions of the outlets 45 on the outer peripheral part side are shifted in the axial direction Da at different positions in the circumferential direction Dc.

FIG. 3 to FIG. 6 are cross-sectional views of the meridian plane shape of the upper half part of the impeller 13 at different positions in the circumferential direction Dc. As illustrated in FIG. 3 , in the meridian plane shape of the impeller 13 at a first position, the outlet 45 side of an impeller flow channel 34-1 is located the closest to the hub 31 in the axial direction Da with respect to a reference impeller flow channel 34-0. At this time, a height H1 of the outlet 45 in the axial direction Da is shorter than a height H of the reference impeller flow channel 34-0. As illustrated in FIG. 4 , in the meridian plane shape of the impeller 13 at a second position, the outlet 45 side of an impeller flow channel 34-2 is located a little closer to the hub 31 relative to a middle position between the hub 31 and the shroud 32 in the axial direction Da with respect to the reference impeller flow channel 34-0. At this time, a height H2 of the outlet 45 in the axial direction Da is shorter than the height H of the reference impeller flow channel 34-0.

As illustrated in FIG. 5 , in the meridian plane shape of the impeller 13 at a third position, the outlet 45 side of an impeller flow channel 34-3 is a little closer to the shroud 32 relative to the middle position between the hub 31 and the shroud 32 in the axial direction Da with respect to the reference impeller flow channel 34-0. At this time, a height H3 of the outlet 45 in the axial direction Da is shorter than the height H of the reference impeller flow channel 34-0. As illustrated in FIG. 6 , in the meridian plane shape of the impeller 13 at a fourth position, the outlet 45 side of an impeller flow channel 34-4 is located the closest to the shroud 32 in the axial direction Da with respect to the reference impeller flow channel 34-0. At this time, a height H4 of the outlet 45 in the axial direction Da is shorter than the height H of the reference impeller flow channel 34-0.

Note that in the meridian plane shape of the impeller 13 at the respective positions, the heights H1, H2, H3, and H4 of the impeller flow channels 34 (outlets 45) in the axial direction Da may be either the same or different.

FIG. 7 is a side view of a main part of the impeller, illustrating the outlet of the impeller according to the present embodiment.

As illustrated in FIG. 7 , the positions of the outlets 45 in the impeller flow channels 34 of the impeller 13 are shifted in the axial direction Da at different positions in the circumferential direction Dc. Therefore, the shape of the outlet 45 when the impeller 13 is viewed from the outer peripheral part side in the radial direction Dr is arranged along an inclination line L2 with a predetermined inclination angle θ with respect to a reference line L1 along the circumferential direction Dc. At this time, the passage shape of the outlet 45 is a quadrangle (parallelogram).

The blade 33 includes a main body part 33 a and two extension parts 33 b and 33 c. The main body part 33 a is fixed to the hub 31 on one side in the axial direction Da and fixed to the shroud 32 on the other side. The extension part 33 b extends to be tapered along the shroud 32 from the main body part 33 a to one side in the circumferential direction Dc and is fixed to the shroud 32. The extension part 33 c extends to be tapered along the hub 31 from the main body part 33 a to the other side in the circumferential direction Dc and is fixed to the hub 31. The impeller flow channel 34 (outlet 45) is formed in a quadrangle (parallelogram) shape in a manner of being sectioned by a surface 34 a of the main body part 33 a of the blade 33, a surface 34 b of the extension part 33 b, a surface 34 c of the main body part 33 a of the adjacent blade 33, and a surface 34 d of the extension part 33 c. Since the impeller 13 rotates to the other side in the circumferential direction Dc (left side in FIG. 7 ), the surface 34 d of the blade 33 serves as a pressure surface and the surface 34 b thereof serves as a suction surface.

In this case, as for the impeller flow channels 34 (outlets 45), the shapes of the impeller flow channels 34-1, 34-2, 34-3, and 34-4 at the respective positions in FIG. 3 to FIG. 6 change continuously in a longitudinal direction of the impeller flow channel 34 and thus, the surfaces 34 b and 34 d are formed and the outlet 45 becomes a quadrangle (parallelogram). As for the impeller flow channels 34 (outlets 45), the shapes of the impeller flow channels 34-1, 34-2, 34-3, and 34-4 at the respective positions in FIG. 3 to FIG. 6 may be changed in steps in the longitudinal direction of impeller flow channel 34.

FIG. 8 is a schematic view illustrating the blade shape on the hub side in the impeller. FIG. 9 is a schematic view illustrating the blade shape in a middle part between the hub and the shroud in the impeller. FIG. 10 is a schematic view illustrating the blade shape of on the shroud side in the impeller.

As mentioned above, the outlet 45 of the impeller 13 has a hexagonal shape along the inclination line L2, so the blades 33 have different thicknesses at different positions in the axial direction Da. FIG. 8 illustrates the blade shape on the hub 31 side, FIG. 9 illustrates the blade shape at the middle part between the hub 31 and the shroud 32, and FIG. 10 illustrates the blade shape on the shroud 32 side. As illustrated in FIG. 8 to FIG. 10 , the thickness of the blade 33 on the outer peripheral part side (outlet 45) in the middle part between the hub 31 and the shroud 32 is smaller than the thickness on the outer peripheral part side (outlet 45) on the hub 31 side and the thickness on the outer peripheral part side (outlet 45) on the shroud 32 side.

In other words, as illustrated in FIG. 7 , a thickness C1 of the blade 33 on the outer peripheral part side (outlet 45 side) on the hub 31 side and a thickness C3 on the outer peripheral part side (outlet 45 side) on the shroud 32 side are the same. A thickness C2 of the blade 33 on the outer peripheral part side (outlet 45 side) in the middle part between the hub 31 and the shroud 32 is set to be smaller than the thickness C1 on the hub 31 side and the thicknesses C1 and C3 on the shroud 32 side.

As illustrated in FIG. 8 to FIG. 10 , the thickness of the blade 33 on the hub 31 side and the thickness thereof on the shroud 32 side gradually increase from the axial line O side toward the outer peripheral part side of the impeller 13. Therefore, the impeller flow channel 34 has approximately the same width on the hub 31 side and on the shroud 32 side, and the rapid expansion of the passage area is suppressed in the impeller flow channel 34 from the inlet 44 to the outlet 45. As a result, since the rapid expansion of the passage area in the impeller flow channel 34 of the impeller 13 is suppressed, the separation of the working fluid from the inner surface of the impeller flow channel 34 is suppressed, thereby reducing losses.

On the other hand, the blade 33 has a substantially constant thickness in the middle part between the hub 31 and the shroud 32 from the axial line O side to the outer peripheral part side of the impeller 13. The impeller 13 compresses the working fluid more efficiently in the region in the middle part between the hub 31 and the shroud 32 than in the region on the hub 31 side or in the region on the shroud 32 side in impeller flow channel 34. Therefore, securing the sufficient capacity in this region can secure the head (pressure) efficiency and improve the efficiency.

The thickness of the blade 33 on the outlet 45 side in the middle part between the hub 31 and the shroud 32 is smaller than the thickness on the outlet 45 side on the hub 31 side and the shroud 32 side. The outlets 45 provided in the peripheral part of the impeller 13 will then be substantially continuous in the circumferential direction Dc. In other words, the outlets 45 are interrupted only by the thickness of the main body part 33 a in the blade 33. As a result, the discharge of the working fluid from each outlet 45 is less likely to be interrupted, resulting in smaller pressure fluctuations and suppressing the occurrence of pressure pulsations.

The impeller 13 in this embodiment is manufactured by cutting, but the manufacturing method is not limited. For example, the manufacture may be performed by a three-dimensional additive manufacturing method such as additive manufacturing (AM).

Modifications

FIG. 11 is a side view of a main part of an impeller according to a first modification, illustrating an outlet of the impeller. FIG. 12 is a side view of a main part of an impeller according to a second modification, illustrating an outlet of the impeller. FIG. 13 is a side view of a main part of an impeller according to a third modification, illustrating an outlet of the impeller.

In a first modification, as illustrated in FIG. 11 , an impeller 13A is a closed impeller including the hub 31, the shroud 32, and a plurality of blades 33A, and the hub 31, the shroud 32, and the blades 33A form a plurality of impeller flow channels 34A. The impeller 13A varies in meridian plane shape in the circumferential direction Dc. In other words, in the impeller flow channels 34A of the impeller 13A that are sectioned by the hub 31, the shroud 32, and the blades 33A, the positions of the outlets 45 on the outer peripheral part side are shifted in the axial direction Da at different positions in the circumferential direction Dc.

As illustrated in FIG. 3 to FIG. 6 , the meridian plane shape of the impeller 13A is different at different positions in the circumferential direction Dc. In other words, the meridian plane shape of the impeller 13A changes in the order of FIG. 3 , FIG. 4 , FIG. 5 , and FIG. 6 from the upstream side in the rotating direction. The change of the meridian plane shape in the impeller 13A is similar to that in the embodiment described above. The shape of the outlet 45 when the impeller 13A is viewed from the outer peripheral part side in the radial direction Dr is arranged along an inclination line L3 with a predetermined inclination angle θ with respect to the reference line L1 along the circumferential direction Dc. At this time, the passage shape of the outlet 45 is a hexagonal shape.

The blade 33A has the main body part 33 a and the two extension parts 33 b and 33 c. The main body part 33 a is fixed to the hub 31 on one side in the axial direction Da and fixed to the shroud 32 on the other side. The extension part 33 b extends to be tapered along the shroud 32 from the main body part 33 a to one side in the circumferential direction Dc and is fixed to the shroud 32. The extension part 33 c extends to be tapered along the hub 31 from the main body part 33 a to the other side in the circumferential direction Dc and is fixed to the hub 31. The impeller flow channel 34A (outlet 45) is formed in a hexagonal shape in a manner of being sectioned by the surface 34 a of the main body part 33 a of the blade 33A, the surface 34 b of the extension part 33 b, the surface 34 c of the shroud 32, the surface 34 d of the main body part 33 a of the adjacent blade 33A, a surface 34 e of the extension part 33 c, and a surface 34 f of the hub 31.

In a second modification, as illustrated in FIG. 12 , an impeller 13B is a closed impeller including the hub 31, the shroud 32, and a plurality of blades 33B, and the hub 31, the shroud 32, and the blades 33B form a plurality of impeller flow channels 34B. The impeller 13B varies in meridian plane shape in the circumferential direction Dc. In other words, in the impeller flow channels 34B of the impeller 13B that are sectioned by the hub 31, the shroud 32, and the blades 33B, the positions of the outlets 45 on the outer peripheral part side are shifted in the axial direction Da at different positions in the circumferential direction Dc.

As illustrated in FIG. 3 to FIG. 6 , the meridian plane shape of the impeller 13B is different at different positions in the circumferential direction Dc. In other words, the meridian plane shape of the impeller 13A changes in the order of FIG. 6 , FIG. 5 , FIG. 4 , and FIG. 3 from the upstream side in the rotating direction. The change in the meridian plane shape of the impeller 13B is opposite to that in the first modification described above. The shape of the outlet 45 when the impeller 13B is viewed from the outer peripheral part side in the radial direction Dr is arranged along an inclination line L4 that is inclined with respect to the reference line L1 along the circumferential direction Dc. At this time, the passage shape of the outlet 45 is a parallelogram. In other words, the heights of the outlets 45 along the axial direction Da are the same height in the meridian plane shape of the impeller 13B at the different positions in the circumferential direction Dc.

In a third modification, as illustrated in FIG. 13 , an impeller 13C is a closed impeller including the hub 31, the shroud 32, and a plurality of blades 33C and 33D, and the hub 31, the shroud 32, and the blades 33C and 33D form the impeller flow channels 34A and 34B. The impeller 13C varies in meridian plane shape in the circumferential direction Dc. In other words, in the impeller flow channels 34A and 34B of the impeller 13C that are sectioned by the hub 31, the shroud 32, and the blades 33C and 33D, the positions of the outlets 45 on the outer peripheral part side are shifted in the axial direction Da at different positions in the circumferential direction Dc.

In other words, the impeller 13C is a combination of the first embodiment (FIG. 7 ) and the second modification (FIG. 12 ), in which the blades 33C and 33D in different shapes are disposed alternately in the circumferential direction Dc so that the impeller flow channels 34A and 34B in different shapes are arranged alternately in the circumferential direction Dc.

Operation Effects of Embodiment

The impeller according to a first aspect includes the hub 31 having a circular plate shape with the axial line O as the center, the shroud 32 disposed to face the hub 31 in the axial direction Da, the blades 33, 33A, 33B, 33C, and 33D disposed with a space from each other in the circumferential direction Dc between the hub 31 and the shroud 32, in which the meridian plane shape is different in the circumferential direction Dc.

In the impeller according to the first aspect, the meridian plane shape of the impellers 13, 13A, 13B, and 13C is different in the circumferential direction Dc; therefore, for example, by shifting and deviating a particular position of the outlet 45 to the hub 31 side or the shroud 32 side, the outlets 45 become substantially continuous in the circumferential direction Dc. In other words, the outlets 45 are interrupted only by the thickness of the main body part 33 a of the blades 33, 33A, 33B, 33C, and 33D, so that the discharge of the working fluid from each outlet 45 is interrupted less easily and pressure fluctuations become smaller, and since the pressure fluctuations at the outlets 45 in the circumferential direction are reduced, pressure pulsations can be suppressed.

In the impeller according to a second aspect, in the impeller flow channels 34, 34A, and 34B sectioned by the hub 31, the shroud 32, and the pairs of blades 33, 33A, 33B, 33C, and 33D, the positions of the outlets 45 on the outer peripheral part side are shifted in the axial direction Da at the different positions in the circumferential direction Dc. Thus, the outlets 45 can be brought as close to each other as possible in the circumferential direction Dc, which reduces pressure fluctuations at the outlets 45, and accordingly, the occurrence of pressure pulsations can be suppressed.

In the impeller according to a third aspect, the outlets 45 are arranged along the inclination lines L2, L3, and L4 with the predetermined inclination angle θ with respect to the reference line L1 along the circumferential direction Dc. This allows the outlets 45 to be as close to each other as possible in the circumferential direction Dc.

In the impeller according to a fourth aspect, the outlet 45 has the passage with the quadrangle shape. Thus, the area blocking the outlet 45 by the blade 33 can be reduced in the circumferential direction Dc, thereby effectively suppressing the pressure pulsations in the circumferential direction Dc and improving the performance.

In the impeller according to a fifth aspect, the outlet 45 has the passage with a hexagonal shape. Thus, the area blocking the outlet 45 by the blade 33 can be reduced in the circumferential direction Dc, thereby effectively suppressing the pressure pulsations in the circumferential direction Dc and improving the performance.

In the impeller according to a sixth aspect, the thickness C2 of each of the blades 33, 33A, 33B, 33C, and 33D on the outer peripheral part side in the middle part between the hub 31 and the shroud 32 is smaller than the thickness C1 on the outer peripheral part side on the hub 31 side and the thickness C3 on the outer peripheral part side on the shroud 32 side. Thus, the thickness of each of the blades 33, 33A, 33B, 33C, and 33D on the hub 31 side and the shroud 32 side is gradually increased to the outer peripheral part side, thereby suppressing the rapid expansion of the passage area of the impeller flow channels 34, 34A, and 34B. As a result, the separation of the working fluid from the inner surface of the impeller flow channel 34 is suppressed and losses can be reduced. On the other hand, since the thickness of the blades 33, 33A, 33B, 33C, and 33D in the middle part between the hub 31 and the shroud 32 is substantially constant to the outer peripheral part side, securing the sufficient capacity in this region can secure the head (pressure) efficiency and improve the efficiency.

The impeller according to a seventh aspect is the closed impeller in which the blades 33, 33A, 33B, 33C, and 33D are fixed to the hub 31 on one side and fixed to the shroud 32 on the other side. Thus, the pressure fluctuations at the outlets 45 of the impellers 13, 13A, 13B, and 13C are reduced, and the occurrence of pressure pulsations can be suppressed.

The rotary machine according to an eighth aspect includes any of the impellers 13, 13A, 13B, and 13C. Thus, the pressure fluctuations at the outlets 45 of the impellers 13, 13A, 13B, and 13C are reduced and the occurrence of pressure pulsations can be suppressed, and accordingly, the efficiency of the rotary machine can be improved.

In the embodiment described above, the meridian plane shape of the impellers 13, 13A, 13B, and 13C changes in the circumferential direction Dc in the order of FIG. 3 to FIG. 6 , or vice versa, and the shape of the outlet 45 is hexagonal or quadrangle, but the shape is not limited to this shape. The impeller may have any shape as long as the meridian plane shape of the impeller varies at different positions in the circumferential direction Dc.

In the embodiment described above, the impellers 13, 13A, 13B, and 13C are the closed impellers, but may alternatively be open impellers with the hub and blades rotatable with respect to the shroud.

In the aforementioned embodiment, the rotary machine is described as a centrifugal compressor, but may alternatively be any other rotary machine.

REFERENCE SIGNS LIST

-   -   10 Centrifugal compressor (rotary machine)     -   11 Casing     -   12 Rotary shaft     -   13, 13A, 13B, 13C Impeller     -   21 First space part     -   22 Second space part     -   23 Inlet passage     -   24 Outlet passage     -   31 Hub     -   32 Shroud     -   33, 33A, 33B, 33C, 33D Blade     -   34, 34A, 34B Impeller flow channel     -   41 Through-hole     -   42 Main surface     -   43 Opposing surface     -   44 Inlet     -   45 Outlet 

1. An impeller comprising: a hub having a circular plate shape with an axial line as a center; a shroud disposed to face the hub in a direction of the axial line; and a plurality of blades disposed with a space from each other in a circumferential direction between the hub and the shroud, wherein a meridian plane shape of the impeller differs in the circumferential direction.
 2. The impeller according to claim 1, wherein in a flow channel sectioned by the hub, the shroud, and a pair of the blades, a position of an outlet on an outer peripheral part side is shifted from one another in the direction of the axial line at a different position in the circumferential direction.
 3. The impeller according to claim 2, wherein the outlet is arranged along an inclination line with a predetermined inclination angle with respect to a reference line along the circumferential direction.
 4. The impeller according to claim 3, wherein the outlet has a passage with a quadrangle shape.
 5. The impeller according to claim 3, wherein the outlet has a passage with a hexagonal shape.
 6. The impeller according to claim 1, wherein a thickness of the blade on an outer peripheral part side in a middle part between the hub and the shroud is smaller than a thickness on the outer peripheral part side on the hub side and a thickness on the outer peripheral part side on the shroud side.
 7. The impeller according to claim 1, wherein the impeller is a closed impeller in which the blades are fixed to the hub on one side and fixed to the shroud on the other side.
 8. A rotary machine comprising the impeller according to claim
 1. 